title: 5'-Methylthioadenosine nucleosidase. Purification and characterization of the enzyme from Lupinus luteus seeds.
abstract: 5'-Methylthioadenosine nucleosidase (EC 3.2.2.9), the enzyme which catalyzes hydrolytic cleavage of 5'-methylthioadenosine with the formation of adenine and 5'-methylthioribose, has been purified to homogeneity from Lupinus luteus seeds. The nucleosidase has a native molecular weight of 62 000 and consists of two identical subunits, as judged by gel filtration and dodecylsulfate/polyacrylamide gel electrophoresis. The nucleosidase exhibits highest specificity towards the natural substrate with a Km of 4.1 X 10(-7) M for 5'-methylthioadenosine. It does not cleave adenine from S-adenosylhomocysteine. Among the synthetic analogs of 5'-methylthioadenosine tested, eleven compounds appear to be able to substitute as substrates. Furthermore, the enzyme can liberate hypoxanthinine from six inosyl (deaminated) derivatives obtained by enzymatic deamination of 5'-methylthioadenosine and its synthetic analogs. The Km for 5'-methylthioinosine is 55 microM, and the maximal velocity about 50-times lower than for 5'-methylthioadenosine. The reaction catalyzed by the nucleosidase can be inhibited by adenine (Ki = 11 microM), 3-deazaadenine (Ki = 19 microM), and 9-erythro(2-hydroxyl-3-nonyl)adenine (ki = 37 microM).
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D008970:Molecular Weight; D010430:Pentosyltransferases / Q000302:isolation & purification*; D011683:Purine-Nucleoside Phosphorylase / Q000302:isolation & purification* / Q000378:metabolism; D012639:Seeds / Q000201:enzymology*; D013379:Substrate Specificity; D013872:Thionucleosides / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D013872:Thionucleosides; C021714:2-methylthioadenosine; D010430:Pentosyltransferases; D011683:Purine-Nucleoside Phosphorylase; C021784:5'-methylthioadenosine phosphorylase; D000241:Adenosine